docs: def handle_namespace_pattern(self, line: str, position: int, tokens: ParseResults) -> ParseResults:
          """Handle statements like ``DEFINE NAMESPACE X AS PATTERN "Y"``.
  
          :raises: RedefinedNamespaceError
          """
          namespace = tokens['name']
          self.raise_for_redefined_namespace(line, position, namespace)
          self.namespace_to_pattern[namespace] = re.compile(tokens['value'])
          return tokens